Darvish, scratched Tuesday night because of neck discomfort, threw a side session Friday before the Rangers opened a three-game series in Washington.
''I felt as good as the bullpen session that I had in Detroit. No discomfort whatsoever,'' Darvish said through a translator.
Darvish is 4-2 with a 2.35 ERA and 71 strikeouts in 61 1-3 innings.
He didn't pitch for three weeks in spring training because of a stiff neck, which pushed back his first start of the season to April 6.